Surveying involves the determination of unknown positions, surfaces or volumes of objects or setting out of known coordinates using angle and distance measurements taken from one or more positions. In order to perform these measurements, a surveying device being of the type referred to as a total station, comprising a combination of electronics and optics, is frequently used. A total station can be provided with a computer or processing or control unit with writable information for measurements to be performed and for storing data obtained during the measurements. A total station may calculate the position of a target in a fixed ground-based coordinate system.
A tracking system can be used in surveying in order to search for, track, and/or follow targets or objects having or being reflective targets or objects, which prisms are capable of reflecting light impinging thereon after having been emitted by a transmitter, and which reflected light is received by a receiver. The reflective targets or objects can for example comprise reflective prisms, foils, or the like. Such a tracking system may sense the angular direction to the target, whereby the movement of a target having speeds possibly up to a few meters per second or more may be tracked or followed. The tracking system may thereby be used to aim a measuring instrument towards a desired target or object, or in other words, to align the instrument sighting axis of the measuring instrument with the current direction to the target relatively to the measuring instrument.
In the transmitter of a device such as a tracker or laser pointer, a coaxial optic configuration 150 is usually employed, illustrated in the schematic view in FIG. 16, typically including components such as an objective 157, a prism 155, one or more mirrors 152, one or more lenses 154, collimators 153, apertures (not shown in FIG. 16), and means for adjusting such components (not shown in FIG. 16). The reference numeral 151 indicates the laser. However, such a coaxial optic configuration 150 may be expensive due to a relatively high cost of such components, which can entail a relatively high overall cost of the device. The coaxial optic configuration 150 can entail optical effects such as shadows of the prism 155 and reflections on the prism 155 back to the receiver, i.e. crosstalk, which may degrade the performance of the operation of the device. The coaxial optic configuration 150 may require a collimation element or elements 153, as illustrated in FIG. 16, for collimation of the laser beam 156. In a coaxial optic configuration such as illustrated in FIG. 16, a coherent optical radiation source such as a laser may be required in order to achieve a beam of optical radiation or light that is focused through the coaxial optic such that only a limited amount of light or no light is ‘spilled’ that may be received by the receiver or sensor. The use of laser 151 can entail a limitation of laser spot size and non-homogeneity of the laser beam 156. The laser may be required to cover the field of view of the receiver, which may be about 2°. Laser beams may be non-homogeneous due to spatial coherence and diffraction effects at apertures of the laser source.